The present invention relates to a noise reduction circuit for a sound reproduction system and, more particularly, to an adaptive noise reduction circuit for a hearing aid.
A common complaint of hearing aid users is their inability to understand speech in a noisy environment. In the past, hearing aid users were limited to listening-in-noise strategies such as adjusting the overall gain via a volume control, adjusting the frequency response, or simply removing the hearing aid. More recent hearing aids have used noise reduction techniques based on, for example, the modification of the low frequency gain in response to noise. Typically, however, these strategies and techniques have not achieved as complete a removal of noise components from the audible range of sounds as desired.
In addition to reducing noise effectively, a practical ear-level hearing aid design must accommodate the power, size and microphone placement limitations dictated by current commercial hearing aid designs. While powerful digital signal processing techniques are available, they require considerable space and power such that most are not suitable for use in a hearing aid. Accordingly, there is a need for a noise reduction circuit that requires modest computational resources, that uses only a single microphone input, that has a large range of responses for different noise inputs, and that allows for the customization of the noise reduction according to a particular user's preferences.